CISC 332 Lecture Notes - Lecture 8: Result Set, Boolean Expression, Unique Key
10 Feb 2018
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Tuples selected for inclusion from r in the result set are those that satisfy the select condition. Where is a boolean expression specified on attribute values. Find all students who are not yet 30 years old: Find all students who are over 30 and failing. Result 30 and mark >30 students. Same number of attributes as the original table has. Degree = # of attributes in Attributes will be in the same order as those specified in attr list. # of tuples will be less than or equal to something - see slides. Attributes (columns) selected for inclusion in result set are based on those in the attribute list. Ex: list the students by student number and mark only. Would come back with just the two columns. If you omit your primary key, you may get non-unique tuples, so to preserve the relation, duplicates will be removed.
